Inverter Active Discharge with Thermal-Adaptive Gate Pulse Width
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Solution Overview
Problem
Inverters for electric vehicles face challenges in safely and efficiently discharging bulk capacitors during fault conditions, which can lead to excessive stress on power switches due to high voltages and temperature variations, particularly in high electromagnetic field environments.
Innovation Solution
A system and method for controlling active discharge of bulk capacitors in inverters by monitoring temperature, current changes, and filtered currents, adjusting pulse width modulation based on threshold determinations to manage discharge safely and efficiently, using integrated gate drivers and thermal sensors to protect SiC MOSFETs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active discharge of bulk capacitor is performed to reduce high voltage risk, then safety is improved, but stress on power switches increases
Solution Approach 1:
The gate control signal uses dynamic pulse width modulation where the pulse width is adjusted in real-time based on detected temperature and current rate of change. The controller increases pulse width when temperature or current rate of change exceeds thresholds, and decreases it when parameters are within safe ranges, creating a dynamic response that adapts to changing conditions during discharge
Solution Approach 2:
The system changes the pulse width parameter of the gate control signal based on detected temperature and current rate of change. By modulating this parameter dynamically, the system optimizes the discharge process to balance safety requirements with protection of power switches from excessive stress
2Loss of time
If pulse width of gate control signal is increased to speed up discharge, then discharge time is reduced, but temperature and current stress on power switches increases
Solution Approach 1:
The controller continuously detects temperature and current rate of change of the power switch during discharge, comparing these values against predefined thresholds. Based on this feedback, the controller automatically adjusts the pulse width of the gate control signal - increasing it to accelerate discharge when safe, and decreasing it when temperature or current stress approaches dangerous levels
Solution Approach 2:
The system employs dynamic pulse width modulation where the gate signal characteristics change in real-time based on thermal and electrical conditions. This dynamic adjustment allows the system to optimize discharge speed while preventing excessive temperature rise and current stress
3Strength
If traditional resistive discharge method is used, then power switch stress is reduced, but discharge time increases and system complexity increases
Solution Approach 1:
The system uses the power switch itself to perform the discharge function by operating it in a controlled linear region rather than requiring external resistive discharge circuitry. The power switch dissipates the bulk capacitor energy through controlled switching, making the discharge system self-contained and eliminating the need for separate resistive discharge components
Solution Approach 2:
By changing the operating parameters of the power switch (gate pulse width, frequency) during discharge, the system achieves rapid discharge without requiring external resistive elements. The dynamic parameter adjustment allows the switch to handle discharge conditions that would normally require passive resistive circuits
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system reduces discharge time while protecting power switches from excessive temperature and current stress, ensuring safe operation and reducing costs by eliminating resistive elements, thus enhancing inverter reliability and efficiency.
Implementation Method 1
detect a temperature of the power switch, a rate of change in current of the power switch, and a filtered current of the power switch
Implementation Method 2
detect a temperature of the power switch, a rate of change in current of the power switch, and a filtered current of the power switch
Data Source
AI summary
A system includes: an inverter configured to convert DC power from a battery to AC power to drive a motor, wherein the inverter includes: a power switch including a drain terminal, a source terminal, and a gate terminal; and one or more controllers configured to: detect a temperature of the power switch, a rate of change in current of the power switch, and a filtered current of the power switch, and control a pulse width of a gate control signal to the gate terminal based on the detected temperature of the power switch, the detected rate of change in current of the power switch, and the detected filtered current of the power switch.